The present invention relates to diagnostic devices for analyte assay. More particularly it relates to devices and methods utilizing filter means for testing biological fluids to detect the presence of analytes such as bacterial, viral, parasitic, or fungal antigens and immunoglobulins, hormones, serum proteins, drugs, and the like.
At the present time there are a number of devices and procedures disclosed for diagnosing for the presence of such analytes by means of reaction occurring on filters but they are either too complex, costly, inaccurate, time-consuming or a combination of such factors.
For example, U.S. Pat. No. 3,888,629 discloses a reaction cell having a matrix pad for carrying out immunoassays. The pad serves as the means for retaining the reagents and as the site in which the reaction occurs and one or more of the fluid reagents are added to the pad and pass therethrough to the absorbent material directly below. In addition to the many time-consuming steps required to process the pad to determine the results of the test; including removing it from the device, such device is essentially limited to isotopic tests. It is not practical for nonisotopic tests such as enzyme-linked immunoassays, since the device requires removal of the absorbent pad for viewing. Moreover, certain biological fluids, such as blood sera, contain particulate and/or colored matter which tend to remain on the surface of the matrix pad and thus make it difficult, if not impossible, to obtain an accurate reading in nonisotopic immunoassay procedures. Further, by passing the reagents directly through the entire surface area of the matrix pad there is often poor separation of the analyte since the absorbent pad is very thin (thereby affording only a very short distance for a separation to occur) and there is limited concentration of analyte at any location on or in the pad.
Efforts to improve such device are reflected in U.S. Pat. Nos. 4,246,339 and 4,407,943 which try to limit the area of the fiber through which one or more of the reagents must pass. Here again, however, there is flow directly through the thin filter to the absorbent material below the filter resulting again in poor separation and difficulty in obtaining accurate readings when specimens are being tested which contain particulate and/or colored matter which is retained on the surface of the filter.